Plasma processing apparatus

ABSTRACT

A plasma processing apparatus carries out plasma processings such as etching, ashing and CVD on large substrates such as semiconductor device substrates and glass substrates for liquid crystal display panels, etc. The plasma processing apparatus having microwave generator 26, a microwave guide path 23, a microwave window 4 and a reaction room 2, etc., has a dielectric sheet 21 disposed to confront the microwave window 4 through a hollow area 20. The dielectric sheet is divided into multiple dielectric sheets 21a, 21b, and the microwave guide path 23a, 23b are connected to the divided dielectric sheets 21a, 21b. This simple structure enables the stable and uniform plasma processing on large substrates such as glass substrates for liquid crystal display panels.

TECHNICAL FIELD

The present invention relates to a plasma processing apparatus which issuitable for carrying out the etching, ashing and CVD processes by usingplasma on semiconductor device substrates, glass substrates for liquidcrystal display (LCD) panels, and the like.

BACKGROUND ART

Plasma of reactive gas is used widely in the fabricating process of LSIand LCD devices. Particularly, the dry etching technique using plasma isan indispensable fundamental technique for the fabricating process ofLSI and LCD devices.

As excitation means for generating plasma, the RF (high frequency) of13.56 MHz is often used, and the microwave is also used recently. Thisis attributable to the advantages of the generation of low temperatureand high-density plasma and the simplicity of the structure andoperation of the apparatus.

However, it is difficult for plasma processing apparatus using themicrowave to generate uniform microwave plasma over a large area, andtherefore it is difficult to process large semiconductor substrates andLCD glass substrates uniformly.

In regard to this matter, the applicant of the present invention hasproposed a scheme of using a dielectric sheet for a plasma processingapparatus that is capable of producing uniform microwave plasma over alarge area, as disclosed in Japanese Patent Application Laid-Open No.62-5600 and No. 62-99481.

FIG. 1, FIG. 2 and FIG. 3 are a schematic plan view, a partialcross-sectional view along the line A--A, and a partial cross-sectionalview along the line B--B, respectively, of the plasma processingapparatus having the dielectric sheet proposed in the above-mentionedpatent publication.

In the plasma processing apparatus shown in these figures, the microwavegenerated by a microwave generator 26 is directed by a microwave guidepath 23 into a dielectric sheet 21. The microwave propagated in thedielectric sheet 21 forms an electric field in a hollow area 20 beneathit. The electric field penetrates a microwave window 4 and enters areaction room 2, in which reactive gas is excited and plasma isgenerated. By the generated plasma, the surface of a sample S issubjected to the plasma processing.

The dielectric sheet 21 consists of an entry section 211, a fan-tailedsection 212 and a flat section 213. The microwave is led from themicrowave guide path 23 into the dielectric sheet 21 as follows. At theentry section 211, the microwave is led from the waveguide into thedielectric sheet. It is expanded in the transverse direction in thefan-tailed section 212. The expanded microwave is led into the flatsection 213. Based on this structure, the microwave can be propagatedwith a uniform transverse distribution in the large flat section 213.

The plasma processing apparatus having this dielectric sheet enables themicrowave to propagate uniformly to the large flat section 213, and bywidening the microwave window 4 and microwave lead-in opening 3 whichconfront the flat section 213, it is possible to generate microwaveplasma of large area in the reaction room 2.

In recent years, large glass substrates are used for LCD panels, andthere are intense demands for apparatus that are capable of uniformlyprocessing glass substrates of 400-by-400 mm or larger. Plasmaprocessing apparatus having this dielectric sheet can generatelarge-area plasma by having a large dielectric sheet, microwave windowand microwave lead-in opening, as mentioned above.

However, when the area of the dielectric sheet is increased steadily,the following problem will emerge. If the dielectric sheet has its widthwidened too much, with the fan-tailed section 212 being unchanged inlength, the dielectric sheet of the fan-tailed section fans out at alarge angle in the transverse direction. Therefore, the microwave cannotbe expanded uniformly in the transverse direction of the dielectricsheet, resulting in a weak electric field of the microwave at the endsin the transverse direction of the dielectric sheet and an unevendistribution of plasma in the transverse direction of the dielectricsheet.

If the dielectric sheet is made too long, the electric field of themicrowave diminishes sharply along the propagation direction of themicrowave, resulting in an uneven distribution of plasma in themicrowave propagation direction.

In order to introduce the microwave uniformly in the transversedirection of the dielectric sheet, it is necessary for the dielectricsheet of the fan-tailed section to fan out at a smaller angle. However,a smaller angle results in a longer fan-tailed section.

The reduction of the electric field strength of the microwave along thepropagation direction of the microwave can be alleviated by widening thespace between the dielectric sheet and the microwave window so as toweaken the coupling of the microwave and plasma. However, a weakcoupling reduces the plasma density significantly and decreases theplasma processing rate.

Uneven propagation of the microwave due to an increased area of thedielectric sheet results in an uneven temperature rise caused by theabsorption of the microwave at each portion of the dielectric sheet. Onthis account, the dielectric sheet surface has an uneven temperaturedistribution, which causes the deformation of dielectric sheet anddeteriorates the repeatability of the plasma processing rate.

The present invention is intended to deal with the foregoing problems,and its object is to provide a plasma processing apparatus that issimple in structure and capable of carrying out the stable and uniformplasma processing on large substrates such as glass substrates forliquid crystal display (LCD) panels.

DISCLOSURE OF THE INVENTION

The inventive plasma processing apparatus has its dielectric sheet,which confronts the microwave window, divided into multiple sheets, withthe divided dielectric sheets being connected to one or more microwavegenerators through a microwave guide path(s). Based on this structure,each dielectric sheet to which the microwave is introduced by amicrowave guide path can have a smaller area, and consequently themicrowave can have a uniform electric field distribution.

FIG. 4, FIG. 8 and FIG. 12 show examples of apparatus having theirdielectric sheet divided in the transverse direction. The detailedstructure of the apparatus will be explained later. As shown in thefigures, the dielectric sheet is divided in the transverse direction andthe microwave is introduced to each divided section, and consequentlythe microwave can be introduced uniformly in the transverse direction ofthe dielectric sheet without making the fan-tailed section of thedielectric sheet longer. In addition, the microwave propagation areadecreases, and the reduction of the electric field strength of themicrowave along the propagation direction can be alleviated.

FIG. 14 shows an example of an apparatus having its dielectric sheetdivided in the microwave propagation direction, and the detailedstructure of the apparatus will be explained later. By dividing thedielectric sheet in the microwave propagation direction and introducingthe microwave into each divided section, the microwave propagationdistance can be reduced and the reduction of the electric field strengthof the microwave along the propagation direction can be alleviated. Inaddition, the microwave propagation area decreases, and the reduction ofthe electric field strength of the microwave at the end in thetransverse direction of the dielectric sheet can be alleviated.

Any of the above-mentioned cases can achieve the uniform propagation ofthe microwave in the dielectric sheet, and the deformation of dielectricsheet and the aggravation of the repeatability of plasma processingcaused by the uneven temperature distribution on the dielectric sheetsurface can be prevented.

As shown in FIG. 8, FIG. 12 and FIG. 14 in the cases of dividing thedielectric sheet, the interference of the microwave propagated in eachdielectric sheet can be alleviated by separating the divided dielectricsheets by means of metallic plates. Based on this structure, even if theplasma generation condition, e.g., the gas flow rate or the internalpressure of reaction room, is varied, the microwave propagation does notvary significantly. Plasma can be generated stably within the prescribedrange of the plasma generation condition.

As shown in FIG. 4, FIG. 8 and FIG. 12, by dividing the dielectric sheetin the transverse direction and introducing the microwave to eachdivided section, it is no longer necessary for the fan-tailed section ofthe dielectric sheet to have a small angle, so the fan-tailed sectioncan be shortened. Consequently, the apparatus can be prevented frombecoming large.

As shown in FIG. 4 and FIG. 8, by connecting a microwave generator tothe divided multiple dielectric sheets by means of a microwave guidepath having branches so that the microwave is propagated by branching,the need of providing multiple microwave generators is eliminated andthe cost of apparatus can be reduced.

As shown in FIG. 12 and FIG. 14, by providing independent microwaveguide paths and microwave generators for the divided dielectric sheetsindividually, the need of the microwave branching section of themicrowave guide path can be eliminated and the structure of theapparatus can be simplified.

BRIEF EXPLANATION OF THE DRAWING

FIG. 1 is a schematic plan view of the conventional plasma processingapparatus, FIG. 2 is a partial cross-sectional view along the line A--Aof the conventional plasma processing apparatus, and FIG. 3 is across-sectional view along the line B--B of the conventional plasmaprocessing apparatus.

FIG. 4 is a schematic plan view of the plasma processing apparatus basedon a first embodiment of this invention, FIG. 5 is a partialcross-sectional view along the line C--C of the plasma processingapparatus of the first embodiment of invention, and FIG. 6 is across-sectional view along the line D--D of the plasma processingapparatus of the first embodiment of invention. FIG. 7 is a graphshowing the result of measurement of the ion current densitydistribution for the plasma processing apparatus of the first embodimentof invention.

FIG. 8 is a schematic plan view of the plasma processing apparatus basedon a second embodiment of this invention, FIG. 9 is a partialcross-sectional view along the line E--E of the plasma processingapparatus of the second embodiment of invention, and FIG. 10 is across-sectional view along the line F--F of the plasma processingapparatus of the second embodiment of invention. FIG. 11 is a graphshowing the result of measurement of the ion current densitydistribution for the plasma processing apparatus of the secondembodiment of invention.

FIG. 12 is a schematic plan view of the plasma processing apparatusbased on a third embodiment of this invention, and FIG. 13 is a partialcross-sectional view along the line G--G of the plasma processingapparatus of the third embodiment of invention.

FIG. 14 is a schematic plan view of the plasma processing apparatusbased on a fourth embodiment of this invention, and FIG. 15 is a partialcross-sectional view along the line H--H of the plasma processingapparatus of the fourth embodiment of invention.

FIG. 16 is a graph showing the result of measurement of the ion currentdensity distribution for the conventional plasma processing apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

The present invention will be explained specifically with reference tothe drawings showing the first embodiment of invention.

FIG. 4 is a schematic plan view of the plasma processing apparatus ofthe first embodiment. This embodiment is intended to divide thedielectric sheet in two parts in its transverse direction.

Introduction of the microwave into the dielectric sheet will beexplained. A microwave guide path 23 is formed of a waveguide. Providedamid the microwave guide path 23 is a microwave distributor (not shown),which supplies the same amount of microwave into two guide paths. Themicrowave guide path 23 connects a microwave generator 26 to the divideddielectric sheets 21a and 21b. The two dielectric sheets 21a and 21b arecovered on their upper surface with a metallic plate 22. The dielectricsheets 21a and 21b are made of fluororesin such as teflon (registeredtrademark). The metallic plate 22 is made of aluminum or the like.

Provided amid the microwave guide path 23 are tuners 24a and 24b whichmake matching of the microwave. Further provided are isolators 25a and25b which remove the reflected microwave. By providing the tuners andisolators on the guide path which is connected to the dielectric sheets21a and 21b, it is possible to adjust the matching of individualdielectric sheets independently and eliminate the adverse influence ofthe respective reflected waves.

The microwave generated by the microwave generator 26 branches into twoamid the microwave guide path 23, and introduced into the dielectricsheets 21a and 21b. The microwaves are introduced at the entry sections211a and 211b from the waveguides into the dielectric sheets, expandedin the transverse direction in fan-tailed sections 212a and 212b, andintroduced into flat sections 213a and 213b. As a result, the microwavesare propagated uniformly in the flat sections 213a and 213b whichconfront the microwave window 4.

FIG. 5 is a partial cross-sectional view taken along the line C--C ofthe plasma processing apparatus of the first embodiment. The reactionchamber and the disposition of the reaction chamber and dielectric sheetwill be explained.

The reaction chamber 1 having a shape of rectangular box is made ofmetal such as aluminum (Al). Formed inside the reaction chamber 1 is areaction room 2. A microwave lead-in opening 3 is formed at the top ofthe reaction chamber 1. The microwave lead-in opening 3 is sealedairtight with an O-ring 9 which is interposed between the microwavewindow 4 and the upper wall of the reaction chamber 1. The microwavewindow 4 has thermal durability and microwave transmissibility, and ismade of a material having small dielectric loss, e.g., quartz glass(SiO₂), alumina (Al₂ O₃), or the like.

Disposed inside the reaction room 2 at the position confronting themicrowave window 4 is a sample stage 7 for mounting a sample S. Thereare provided a gas inlet 5 for supplying the reactive gas and anevacuation port 6 which is connected to an evacuation device (notshown). Formed in a peripheral wall of the reaction chamber 1 is amedium passage 8, in which the medium at a prescribed temperaturecirculates so that the peripheral walls of the reaction chamber 1 ismaintained at a prescribed temperature. A gate valve (not shown) fortransferring in and out a sample S to/from the reaction room 2 is formedin the side wall of the reaction chamber 1.

The dielectric sheets 21a and 21b (not shown) are disposed to confrontthe microwave window 4 thereby to cover the microwave window 4 through ahollow area 20.

FIG. 6 is a schematic cross-sectional view taken along the line D--D ofthe plasma processing apparatus of the first embodiment. The dielectricsheets 21a and 21b are disposed in parallel to confront the microwavewindow 4.

The apparatus of this embodiment has a plasma generation area of500-by-500 mm. The dimensions and materials of the major parts of theapparatus are as follows. The microwave lead-in opening 3 is dimensionedby 500-by-500 mm, and the microwave window 4 is made of a quartz plateof 600-by-600 mm having a thickness of 20 mm. The dielectric sheets 21aand 21b have their flat sections 213a and 213b each dimensioned by600-by-300 mm, and are made of teflon having a thickness of 20 mm.

The method of plasma processing by use of the plasma processingapparatus of this embodiment on the surface of a sample S which isplaced on the sample stage will be explained.

The medium at the prescribed temperature is run to circulate in themedium passage 18. The reaction room 2 is evacuated through theevacuation port 6 until the prescribed pressure, and thereafter thereactive gas is supplied through the gas inlet 5 formed in theperipheral wall to establish the prescribed pressure in the reactionroom 2.

The microwave generator 26 is operated to generate the microwave, andthe generated microwave is introduced into the dielectric sheets 21a and21b by branching into two guide paths amid the microwave guide path 23.By the microwave propagated in the dielectric sheets 21a and 21b, anelectric field is formed in the hollow area 20 below the dielectricsheets. The electric field passes through the microwave windows 4, andit is supplied to the reaction room 2 to generate plasma. The surface ofthe sample S is subjected to plasma processing by this plasma.

For the evaluation of the uniformity of plasma generated by the plasmaprocessing apparatus of this embodiment, the distribution of ion currentdensity was measured. The measurement was conducted in the Z-directionwhich is the microwave propagation direction and the Y-directionperpendicular to it around the center of the sample stage. The measuringposition was at a distance of 100 mm from the microwave window. Plasmageneration was based on the use of Ar gas at a pressure of 10 mTorr andat a microwave power of 3 kW.

A probe of disc electrode of 2.0 mm in diameter made of stainless steelwas used to measure the ion current density. With a d.c. voltage of -50V being applied to the probe against the reaction chamber wall, acurrent i flowing into the probe was measured. The ion current densitywas calculated by dividing the magnitude of current i by the area ofelectrode of the probe.

FIG. 7 is a graph showing the measurement result of the ion currentdensity distribution of this embodiment. FIG. 7 reveals that plasma wasgenerated virtually uniformly. Not only was plasma generated uniformlyin the Y-direction, but it was also generated uniformly in theZ-direction.

Second Embodiment

FIG. 8, FIG. 9 and FIG. 10 are a schematic plan view, a partialcross-sectional view along the line E--E, and a partial cross-sectionalview along the line F--F of the plasma processing apparatus of thesecond embodiment of this invention.

This embodiment is different from the first embodiment only in that thedielectric sheet is divided into dielectric sheets 21a and 21b and thehollow area is divided into hollow areas 20a and 20b by a metallic wall30. Due to the separation of the dielectric sheets 21a and 21b by themetallic wall 30, the microwave is propagated in each of the dielectricsheets 21a and 21b independently. Accordingly, the interference of themicrowaves propagated in the dielectric sheets 21a and 21b isalleviated.

Introduction of the microwave into the dielectric sheets 21a and 21b andgeneration of plasma are identical to the first embodiment. Themicrowave generated by the microwave generator 26 branches into twoguide paths amid the microwave guide path 23, and is introduced into thedielectric sheets 21a and 21b. By the microwaves propagated in thedielectric sheets 21a and 21b, electric fields are formed in the hollowareas 20a and 20b. These electric fields pass through the microwavewindow 4 into the reaction room 2, and plasma is generated.

The apparatus of this embodiment has its plasma generation areadimensioned by 500-by-500 mm, and the dimensions and materials of themajor parts of the apparatus are as follows. The microwave lead-inopening 3 is dimensioned by 500-by-500 mm, and the microwave window 4 ismade of a quartz plate of 600-by-600 mm having a thickness of 20 mm. Thedielectric sheets 21a and 21b have their flat sections 213a and 213beach dimensioned by 600-by-297 mm, and are made of teflon having athickness of 20 mm. The metallic wall 30 is made of aluminum (Al) of 6mm in width.

For the evaluation of the uniformity of plasma generated by the plasmaprocessing apparatus of this embodiment, the distribution of ion currentdensity was measured in the same manner as the first embodiment. Themeasurement was conducted in the Z-direction which is the microwavepropagation direction and the Y-direction perpendicular to it aroundethe center of the sample stage. The measuring position was at a distanceof 100 mm from the microwave window. Plasma generation was based on theuse of Ar gas at a pressure of 10 mTorr and at a microwave power of 3 kWas in the first embodiment.

FIG. 11 is a graph showing the measurement result of the ion currentdensity distribution of this embodiment. Plasma was generated virtuallyuniformly as in the first embodiment.

Third Embodiment

FIG. 12 and FIG. 13 are a schematic plan view and a partialcross-sectional view along the line G--G of the plasma processingapparatus of the third embodiment of this invention. This embodiment isdifferent from the first embodiment only in that a microwave generator26a and microwave guide path 23a are provided for the dielectric sheet21a, and a microwave generator 26b and microwave guide path 23b areprovided for the dielectric sheet 21b.

The microwave generated by the microwave generator 26a is introduced tothe divided dielectric sheet 21a by way of the microwave guide path 23a.Similarly, the microwave generated by the microwave generator 26b isintroduced to the divided dielectric sheet 21b by way of the microwaveguide path 23b. By the microwaves propagated in the dielectric sheets21a and 21b, electric fields are formed in the hollow areas 20a and 20bbelow them. These electric fields pass through the microwave window 4into the reaction room 2, and plasma is generated.

Fourth Embodiment

FIG. 14 and FIG. 15 are a schematic plan view and a partialcross-sectional view along the line H--H of the plasma processingapparatus of the fourth embodiment of this invention.

This embodiment is intended to divide the dielectric sheet into twoparts in the microwave propagation direction. The dielectric sheet isdivided into dielectric sheets 21a and 21b and the hollow area isdivided into hollow areas 20a and 20b.

The microwave generated by the microwave generator 26a is introduced tothe divided dielectric sheet 21a by way of the microwave guide path 23a.Similarly, the microwave generated by the microwave generator 26b isintroduced to the divided dielectric sheet 21b by way of the microwaveguide path 23b. By the microwaves propagated in the dielectric sheets21a and 21b, electric fields are formed in the hollow areas 20a and 20bbelow them. These electric fields pass through the microwave window 4into the reaction room 2, and plasma is generated.

Comparative Example

FIG. 1, FIG. 2 and FIG. 3 are a schematic plan view, a partialcross-sectional view along the line A--A, and a cross-sectional viewalong the line B--B of a conventional plasma processing apparatus. Thestructure and the operating method of the apparatus shown in thesefigures are as described previously.

The apparatus of this comparative example has a plasma generation areaof 500-by-500 mm. The dimensions and materials of the major parts of theapparatus are as follows. The microwave lead-in opening 3 is dimensionedby 500-by-500 mm, and the microwave window 4 is made of a quartz plateof 600-by-600 mm having a thickness of 20 mm. The dielectric sheet 21has its flat sections 213 dimensioned by 600-by-300 mm, and is made ofteflon having a thickness of 20 mm.

For the evaluation of the uniformity of plasma generated by thisconventional plasma processing apparatus, the distribution of ioncurrent density was measured. The measurement was conducted in theZ-direction which is the microwave propagation direction and theY-direction perpendicular to it around the center of the sample stage.

The measuring position was at a distance of 100 mm from the microwavewindow. Plasma generation was based on the use of Ar gas at a pressureof 10 mTorr and at a microwave power of 3 kW.

FIG. 16 is a graph showing the measurement result of the ion currentdensity distribution of this comparative example. FIG. 16 reveals thatthe ion current density decreases at the end of the Y-axis which is thetransverse direction of the dielectric sheet 21. The ion current densityis high on the entry side and decreases gradually in the Z-directionwhich is the microwave propagation direction. Accordingly, theuniformity of plasma distribution was insufficient.

Industrial Applicability

The inventive apparatus which is simple in structure is capable ofgenerating plasma uniformly in a large area. Therefore, it can carry outplasma processings such as etching, ashing and CVD stably and uniformlyon large substrates such as semiconductor device substrates and glasssubstrates for liquid crystal display panels.

We claim:
 1. A plasma processing apparatus comprising a microwavegenerator, a microwave guide path for propagating a microwave, adielectric sheet connected to said microwave guide path, a microwavewindow disposed to confront said dielectric sheet through a hollow area,and a metallic reaction chamber having its microwave lead-in openingsealed airtight with said microwave window, characterized in that saiddielectric sheet is divided into multiple dielectric sheets and saidmicrowave guide path is connected to said divided dielectric sheets. 2.A plasma processing apparatus according to claim 1, characterized inthat said divided multiple dielectric sheets are separated from eachother by a metallic wall.
 3. A plasma processing apparatus according toclaim 1, characterized in that said dielectric sheet is divided in thetransverse direction thereof into multiple dielectric sheets.
 4. Aplasma processing apparatus according to claim 1, characterized in thatsaid microwave generator is a unitary microwave generator and saidapparatus includes a microwave guide path which causes the microwavefrom said unitary microwave generator to branch and to be propagated tosaid multiple dielectric sheets.
 5. A plasma processing apparatusaccording to claim 1, characterized in that said apparatus includesmicrowave guide paths and microwave generators provided independentlyfor said divided multiple dielectric sheets.
 6. A plasma processingapparatus according to claim 1, characterized in that said divideddielectric sheets are two in number.